Alkaline battery having a dual-anode

ABSTRACT

Various embodiments are directed to an electrochemical cell having a non-homogeneous anode. The electrochemical cell includes a container, a cathode forming a hollow cylinder within the container, an anode positioned within the hollow cylinder of the cathode, and a separator between the cathode and the anode. The anode comprises at least two concentric anode portions, defined by different anode characteristics. For example, the two anode portions may contain different surfactant types, which provides the two anode portions with different charge transfer resistance characteristics. By lowering the charge transfer resistance of a portion of an anode located proximate the current collector of the cell (and away from the separator) relative to an anode portion located adjacent the separator, improved cell discharge performance may be obtained.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Non-Provisional patentapplication Ser. No. 16/145,830 filed on Sep. 28, 2018, which isincorporated herein by reference in its entirety.

BACKGROUND

Particularly for bobbin-style electrochemical cells commonly found inalkaline batteries, the positional oxidation of anode particles impactsthe overall performance of the electrochemical cell. In thesebobbin-style cells, a cathode (typically comprising manganese dioxide asan active material in alkaline primary cells) is formed as a generallyhollow tube positioned within a cell container. An anode (typicallycomprising zinc or a zinc composite) is positioned within the hollowinterior of the cathode and is separated from the cathode by aseparator. A current collector (e.g., a nail) is positioned at thecenter of the anode. The entire composition is saturated in a KOHelectrolyte.

As the battery discharges, the zinc particles are oxidized to formnon-reactive zinc oxide particles within the anode. At a theoreticallevel, once the supply of zinc within the anode is exhausted by theconversion of zinc to zinc oxide, the anode is fully discharged.

Alkaline cells are highly efficient at low discharge rates and theconversion of zinc to generally more voluminous zinc oxide occursgenerally uniformly across the cross section of the anode (i.e., betweenthe separator and the current collector). However, as the discharge rateincreases, the conversion of zinc to the higher-volume zinc oxidebecomes increasingly biased toward the separator. Thus, zinc particleswithin the interior of the anode may not be fully utilized duringmoderate and high rate discharge, thereby preventing these zincparticles from contributing to the discharge performance of the cell.Because the anode active material is not fully exhausted, the usefullife of electrochemical cell is diminished at higher drain rates, and anon-negligible portion of the anode zinc is prevented from full useduring discharge.

Various attempts have been made to impede the formation of a zinc oxidebarrier near the separator of alkaline electrochemical cells duringmoderate- and high-rate discharge, however such attempts have generallyresulted in decreased low discharge rate performance. For example,surfactants have been added to coat zinc particles so as to increase acharge transfer resistance of an anode and encourage a more uniform zincto zinc-oxide conversion. However, such surfactants generally increasethe charge transfer resistance in the anode, thereby decreasing theoverall performance of the electrochemical cell.

According, there is a continuing need for products and methods enablinga more efficient usage of anode active materials in electrochemicalcells, particularly those providing balanced cell performancecharacteristics at both low- and high-discharge rates.

BRIEF SUMMARY

Various embodiments address anode discharge non-uniformity and improveefficiency of the anode in moderate- and high-discharge rateapplications by varying characteristics of the anode as a function ofthe distance away from the cell separator. For example, providingdifferent anode surfactant types in different portions of the anode(e.g., an interior portion near the current collector and an exteriorportion near the separator), providing different anode surfactantconcentrations in different portions of the anode, changing the activematerial concentration as a function of the distance away from the cellseparator, providing different gelling agent types and/or differentgelling agent concentrations in different portions of the anode,providing different electrolyte concentrations in different portions ofthe anode, providing different anode additives in different portions ofthe anode, and/or the like. By varying one or more anode characteristicsas a function of the distance away from the separator (e.g., in agradual function, a step-wise function, and/or the like) may providedifferent portions of the anode with different discharge resistances,thereby encouraging a particular discharge profile for the anode thatincreases the overall usage of anode active ingredients during celldischarge.

Various embodiments are directed to an electrochemical cell comprising:a container; a cathode forming a hollow cylinder and having a cathodeouter surface adjacent an inner surface of the container and a cathodeinner surface defining an interior portion of the cathode; an anodepositioned within the interior portion of the cathode, wherein the anodedefines an anode outer surface adjacent the cathode inner surface and acentral portion; a separator disposed between the anode outer surfaceand the cathode inner surface; and an electrolyte; wherein the anodecomprises at least two anode portions, wherein: a first anode portionlocated adjacent the separator and consists of a first anode formulationhaving a first charge transfer resistance; and a second anode portionlocated at the anode central portion consists of a second anodeformulation having a second charge transfer resistance that is lowerthan the first charge transfer resistance.

According to various embodiments, the first anode formulation comprisesa first surfactant and wherein the second anode formulation comprises asecond surfactant, and wherein the first surfactant is different fromthe second surfactant. Moreover, the first surfactant may comprise aphosphate ester surfactant and the second surfactant may comprise asulfonate surfactant. In certain embodiments, the first anode portion isseparated from the second anode portion by a characteristic gradientbetween the first anode portion and the second anode portion. Moreover,the characteristic gradient comprises the first anode formulation andthe second anode formulation, and wherein the proportion of the firstanode formulation to the second anode formulation is at leastsubstantially proportional to a radial location within the anode.

In certain embodiments, the characteristic gradient is continuousbetween the central portion of the anode and the anode outer surface. Invarious embodiments, a quantity of the first anode composition exceeds aquantity of the second anode composition within the anode.

Certain embodiments are directed to a method of forming anelectrochemical cell. In various embodiments, the method comprises:forming a cathode within a container, wherein the cathode is generallycylindrical and defines a cathode outer surface positioned adjacent aninterior surface of the container and a cathode interior surfacedefining an inner portion of the cathode; positioning a separator withinthe inner portion of the cathode; forming a first cylindrical anodeportion adjacent the separator, wherein the first cylindrical anodeportion defines an open interior and the first cylindrical anode portionconsists of a first anode formulation having a first charge transferresistance; and forming a second cylindrical anode portion within theopen interior of the first cylindrical anode portion and wherein thesecond cylindrical anode portion consists of a second anode formulationhaving a second charge transfer resistance that is lower than the firstcharge transfer resistance.

In various embodiments, forming the first anode portion comprisesextruding the first anode formulation having a first surfactant into theinner portion of the cathode; and forming the second anode portioncomprises extruding the second anode formulation having a secondsurfactant into the open interior of the first cylindrical anodeportion, wherein the second surfactant is different from the firstsurfactant. Moreover, the first surfactant may comprise a phosphateester surfactant and the second surfactant may comprise a sulfonatesurfactant. In certain embodiments, forming the first anode portion andforming the second anode portion collectively comprise coextruding thefirst anode portion and the second anode portion. Moreover, forming thefirst anode portion may comprise: extending a plunger into the innerportion of the cathode such that an exterior surface of the plunger isspaced apart from the separator; extruding the first anode portionbetween the exterior surface of the plunger and the separator; removingthe plunger to form the open interior of the first anode portion; andforming the second anode portion comprises extruding the second anodeportion into the open interior of the first anode portion.

In certain embodiments, a quantity of the first anode compositionexceeds a quantity of the second anode composition within the anode.Moreover, forming the second cylindrical anode portion may compriseforming a mixing region between the second cylindrical anode portion andthe first cylindrical anode portion.

Various embodiments are directed to an anode, for example, for use in analkaline battery having a bobbin-style configuration. In certainembodiments, the anode defines an anode outer surface and a centralportion, and the anode is configured to disposed relative to a cathodesuch that the anode outer surface is adjacent to the cathode andseparates the central portion from the cathode. In certain embodiments,the anode comprises a first anode portion defining the anode outersurface, wherein the first anode portion consists of a first anodeformulation having a first charge transfer resistance; and a secondanode portion located at the anode central portion, wherein the secondanode portion consists of a second anode formulation having a secondcharge transfer resistance that is lower than the first charge transferresistance. In certain embodiments, the first anode formulationcomprises a first surfactant and the second anode formulation comprisesa second surfactant that is different from the first surfactant.Moreover, the first anode portion may be separated from the second anodeportion by a characteristic gradient between the first anode portion andthe second anode portion. In various embodiments, the characteristicgradient comprises the first anode formulation and the second anodeformulation, and wherein the proportion of the first anode formulationto the second anode formulation is at least substantially proportionalto a radial location within the anode, or a separation distance from thecathode. In certain embodiments, the characteristic gradient iscontinuous between the central portion of the anode and the anode outersurface. According to various embodiments, a quantity of the first anodecomposition exceeds a quantity of the second anode composition withinthe anode.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Reference will now be made to the accompanying drawings, which are notnecessarily drawn to scale, and wherein:

FIG. 1 is a cross-sectional elevational view of an alkalineelectrochemical cell according to one embodiment;

FIG. 2 is a schematic cross-sectional view of an anode according to oneembodiment; and

FIG. 3 is a cross-sectional elevational view of an alkalineelectrochemical cell according to one embodiment.

FIG. 4 is an illustration of test results from comparative tests of analkaline battery provided according to one embodiment against a controlalkaline cell.

DETAILED DESCRIPTION

The present invention will now be described more fully hereinafter withreference to the accompanying drawings, in which some, but not allembodiments of the invention are shown. Indeed, the invention may beembodied in many different forms and should not be construed as limitedto the embodiments set forth herein. Rather, these embodiments areprovided so that this disclosure will satisfy applicable legalrequirements. Like numbers refer to like elements throughout.

Alkaline electrochemical cells are commercially available in cell sizescommonly known as LR6 (AA), LR03 (AAA), LR14 (C) and LR20 (D). The cellshave a cylindrical shape that complies with the dimensional standardsthat are set by organizations such as the International ElectrotechnicalCommission. The electrochemical cells are utilized by consumers to powera wide range of electrical devices, for example, clocks, radios, toys,electronic games, film cameras generally including a flashbulb unit, aswell as digital cameras. Such electrical devices possess a wide range ofelectrical discharge conditions, such as from low drain to relativelyhigh drain. Due to the increased use of high drain devices, such asdigital cameras, it is desirable for a manufacturer to produce a batterythat possesses desirable high drain discharge properties.

FIG. 1 shows a cylindrical cell 1 in elevational cross-section, with thecell having a nail-type or bobbin-type construction and dimensionscomparable to a conventional LR6 (AA) size alkaline cell. However, it isto be understood that cells according to various embodiments can haveother sizes and shapes, such as a prismatic or button-type shape; andelectrode configurations, as known in the art. The materials and designsfor the components of the electrochemical cell illustrated in FIG. 1 arefor the purposes of illustration, and other materials and designs may besubstituted.

The electrochemical cell 1 includes a container or can 10 having aclosed bottom end 24, a top end 22, and sidewall 26 therebetween. Theclosed bottom end 24 includes a terminal cover 20 including aprotrusion. The can 10 has an inner wall 16. In the embodiment, apositive terminal cover 20 is welded or otherwise attached to the bottomend 24. In one embodiment, the terminal cover 20 can be formed withplated steel for example with a protruding nub at its center region.Container 10 can be formed of a metal, such as steel, which may beplated on its interior with nickel, cobalt and/or other metals oralloys, or other materials, possessing sufficient structural propertiesthat are compatible with the various inputs in an electrochemical cell.A label 28 can be formed about the exterior surface of container 10 andcan be formed over the peripheral edges of the positive terminal cover20 and negative terminal cover 46, so long as the negative terminalcover 46 is electrically insulated from container 10 and positiveterminal 20.

Disposed within the container 10 are a first electrode 18 and secondelectrode 12 with a separator 14 therebetween. First electrode 18 isdisposed within the space defined by separator 14 and closure assembly40 secured to open end 22 of container 10. Closed end 24, sidewall 26,and closure assembly 40 define a cavity in which the electrodes of thecell are housed.

Closure assembly 40 comprises a closure member 42 such as a gasket, acurrent collector 44 and conductive terminal 46 in electrical contactwith current collector 44. Closure member 42 may contain a pressurerelief vent that will allow the closure member to rupture if the cell'sinternal pressure becomes excessive. Closure member 42 can be formedfrom a polymeric or elastomer material, for example Nylon-6,6, aninjection-moldable polymeric blend, such as polypropylene matrixcombined with poly(phenylene oxide) or polystyrene, or another material,such as a metal, provided that the current collector 44 and conductiveterminal 46 are electrically insulated from container 10 which serves asthe current collector for the second electrode 12. In the embodimentillustrated, current collector 44 is an elongated nail or bobbin-shapedcomponent. Current collector 44 is made of metal or metal alloys, suchas copper or brass, conductively plated metallic or plastic collectorsor the like. Other suitable materials can be utilized. Current collector44 is inserted through a hole (e.g., a centrally located hole) inclosure member 42.

First electrode 18 may be a negative electrode or anode. The negativeelectrode includes a mixture of one or more active materials (e.g.,zinc), an electrically conductive material, solid zinc oxide, and/or, insome embodiments, a surfactant. The negative electrode can optionallyinclude other additives, for example a binder or a gelling agent, andthe like.

Although the embodiment of FIG. 1 illustrates the first electrode 18 ashaving generally uniform characteristics, it should be understood thatvarious embodiments comprise a non-uniform anode configuration. Forexample, the first electrode 18 may define a characteristic gradientbetween the outer surface of the first electrode 18 (e.g., proximate theseparator 14) and the inner portion of the first electrode 18 (e.g.,proximate the current collector 44), for example, to separate a firstanode portion (consisting of a first anode formulation) from a secondanode portion (consisting of a second anode formulation). The gradientmay be continuous, thereby gradually changing between a firstcharacteristic and a second characteristic (e.g., by gradually varyingthe relative concentrations of the anode composition having the firstanode characteristic and the anode composition having the second anodecharacteristic) or lock-step, thereby incorporating discrete regionsdefined by different characteristics that may be separated by a boundaryregion. The boundary region may be defined by a discrete boundarybetween adjacent anode compositions, or by a mixing region in whichportions of each of the adjacent anode compositions mix, for example, asa result of processing steps for adding multiple anode compositions intodiscrete regions of the cell.

In certain embodiments, the boundary between adjacent anode compositionsmay be centered relative to the radius of the first electrode 18 (or theboundaries may be spaced equally along the radius of the first electrode18 in embodiments comprising more than 2 anode compositions), or therate of change of a continuous gradient between adjacent anodecompositions may be centered with the center point of the radius of thefirst electrode 18. However, the boundary or center of the changebetween adjacent anode compositions may be skewed toward the separator14 or the current collector 44 in certain embodiments. Differences inquantity between various anode compositions may be defined based ondifferent characteristics, such as based on weight (e.g., weightpercentage of the total weight of the first electrode 18), volume (e.g.,a volume percentage of the total volume of the first electrode 18),thickness (e.g., a radial thickness percentage of the total thickness ofthe first electrode 18; in other words, a percentage of the length ofthe first electrode 18 radius). As an example, the weight of each anodecomposition (e.g., the first anode composition and the second anodecomposition) may be at least substantially equal. As another example,the volume of each anode composition (e.g., the first anode compositionand the second anode composition) may be at least substantially equal.As yet another example, the thickness of each anode composition (e.g.,the first anode composition and the second anode composition) may be atleast substantially equal. It should be understood that more or less ofa particular anode composition may be included within the firstelectrode 18 in certain embodiments (e.g., such that the weight, volume,or thickness of each anode composition is not equal). As one specificexample tested in the experimental tests described below, the quantityof the first anode composition may exceed the quantity of the secondanode composition, by weight.

In certain embodiments, the anode compositions associated with each ofthe anode characteristics may be defined by differences in surfactanttype included within respective anode compositions. For example, a firstanode composition may comprise a first surfactant type and a secondanode composition may comprise a second surfactant type. In suchembodiments, the first electrode 18 may be defined by a gradual changebetween the first anode composition incorporating the first surfactantproximate the separator 14 and the second anode compositionincorporating the second surfactant proximate the current collector 44.As a specific example, the first anode composition incorporating thefirst surfactant, which is incorporated in a portion of the firstelectrode 18 located adjacent the separator 14 may have a higher chargetransfer resistance than the second anode composition incorporating thesecond surfactant and located in a portion of the first electrode 18located adjacent the current collector 44. The first anode compositionincorporating the first surfactant may also have a lower anodeconductivity than the second anode composition incorporating the secondsurfactant. In such an example, the first anode composition may comprisea phosphate ester surfactant, and the second anode composition maycomprise a sulfonate surfactant (e.g., an anionic sulfonate surfactant).It is the inventors' understanding that the inclusion of the phosphateester surfactant (e.g., a nonionic phosphate ester surfactant) in thefirst anode composition causes the first anode composition to have ahigher charge transfer resistance and lower conductivity than the secondanode composition comprising the sulfonate surfactant. By including alow charge transfer resistance portion near the current collector 44 ofthe first electrode 18 and a high charge transfer resistance portionnear the separator 14, the first electrode 18 discharges such that theportion nearer to the current collector 44 discharges first, and indoing so causes the formation of ZnO particles within the portion of thefirst electrode closest to the current collector 44 prior to theformation of ZnO particles closer to the separator 14. ZnO particlesformed close to the separator 14 prior to complete discharge of theportions of the anode closer to the anode's interior may prevent or atleast impede complete discharge of anode active material within theanode interior by blocking the diffusion of electrolyte across theseparator 14. As mentioned, formulating the first electrode (anode) suchthat the portion of the anode near the current collector 44 dischargesprior to the portion of the anode near the separator 14 ensures thatundischarged active material within the first electrode is not blockedfrom discharge by the formation of ZnO proximate the separator 14. Afterthe portion of the first electrode 18 closer to the current collector 44and having a lower charge transfer resistance at least substantiallydischarges, the portion of the first electrode 18 located closer to theseparator 14 and having a higher charge transfer resistance beginsdischarging.

In embodiments in which the gradual change is defined by a lock-stepchange, a first, outer region of the anode (adjacent the separator 14)comprises the first anode composition incorporating the firstsurfactant, and a second, inner region (adjacent the current collector44) comprises the second anode composition incorporating the secondsurfactant. There may be a discrete boundary between the first anodecomposition and the second anode composition, or there may be a smallmixing region located at the boundary between the first anodecomposition and the second anode composition, wherein the mixing regioncomprises both the first surfactant and the second surfactant.

In embodiments in which the gradual change is continuous, the relativeportion of the total anode composition defined by the first anodecomposition and the second anode composition may vary radially withinthe anode. For example, in a portion of the first electrode 18immediately adjacent the separator 14, the anode composition may bedefined entirely (e.g., 100%) or substantially entirely by the firstanode composition comprising the first surfactant, with minimal or notraces (e.g., 0%) of the second anode composition and minimal or notraces of the second surfactant. Moving closer to the current collector44, the percentage of the anode composition comprising the first anodecomposition decreases, and the percentage of the anode compositioncomprising the second anode composition increases, until reaching theportion of the first electrode 18 immediately adjacent the currentcollector 44, where the anode composition may be defined entirely (e.g.,100%) or substantially entirely by the second anode compositioncomprising the second surfactant, with minimal or no traces (e.g., 0%)of the first anode composition and minimal or no traces of the firstsurfactant.

As discussed in co-pending U.S. patent application Ser. No. 15/896,917,filed on Feb. 14, 2018, the contents of which are incorporated herein byreference in their entirety, other characteristics may vary between thefirst anode portion and the second anode portion. For example, thevarying characteristics may be average particle size of an activematerial (e.g., zinc), average active material alloy composition,average concentration of an active material, average concentration of anadditive, average concentration of a surfactant, and/or the like. Asnon-limiting examples, the relative composition of active material as apercentage of the total composition of the first electrode 18 may varyalong the radius of the first electrode 18 (e.g., between the outersurface and the inner portion of the first electrode 18); one or moreactive material particle characteristics (e.g., particle size, surfaceroughness, porosity, and/or the like) may vary along the radius of thefirst electrode 18; the active material alloy type may vary along theradius of the first electrode, the surfactant type may vary along theradius of the first electrode, the relative composition of surfactant asa percentage of the total composition of the first electrode 18 may varyalong the radius of the first electrode 18; one or more particlecharacteristics of one or more inactive materials may vary along theradius of the first electrode 18; and/or the like.

In certain embodiments, the characteristic gradient may be continuous(e.g., as illustrated in FIG. 2 , which illustrates a cross-sectionalschematic diagram of a first electrode 18 according to variousembodiments). In such embodiments, one or more characteristics of thefirst electrode may change gradually, continuously, and/or the likealong the radius of the first electrode 18, as illustrated based on thecontinuous darkening of the first electrode 18 between the currentcollector 44 and the separator 14 in FIG. 2 . For example, inembodiments in which the average particle size of the active materialchanges along the radius of the first electrode, the average particlesize may change continuously as a function of the radial location withinthe first electrode (e.g., following a linear function, an exponentialfunction, a logarithmic function, a polynomial function, and/or thelike) between the outer surface of the first electrode 18 and the innerportion of the first electrode 18. The change need not follow aparticular formula, however the particle size should vary innon-discrete increments along the radius of the first electrode 18. Itshould be understood that similarly continuous changes between a firstanode composition (e.g., having a first surfactant type) and a secondanode composition (e.g., having a second surfactant type) may beprovided.

In other embodiments in which other anode characteristics change alongthe radius of the first electrode 18, the anode characteristics maychange in a manner similar to that discussed in reference to theabove-described continuous change in active material particle size alongthe radius of the first electrode 18. In various embodiments, multiplecharacteristics may change along the radius of the anode to form amultiple characteristics gradient anode composition. For example, theaverage particle size of the active material within the anode may changealong the radius of the anode and the surfactant type may also changealong the radius of the anode. Any of a variety of combinations of anodecharacteristic changes are envisioned to provide an anode havingdesirable characteristics. As a specific example, an anodecharacteristic gradient may define a first surfactant type in a regionof the anode proximate the separator and a first average active materialparticle size in the region of the anode proximate the separator; and asecond surfactant type and a second average active material particlesize in a region of the anode proximate the current collector. Such aconfiguration may desirably provide a lower charge transfer resistancein the region closer to the current collector 44, which may increasehigh-rate discharge service while minimizing gassing in the region nearthe current collector 44.

As discussed in greater detail herein, two or more anode compositionsmay be blended and extruded to form the first electrode such that theportion of the first electrode 18 located proximate the outer surface ofthe first electrode 18 comprises a concentration of a first anodecomposition that is higher than the concentration proximate the innersurface of the first electrode; the portion of the first electrode 18located proximate the inner portion of the first electrode 18 comprisesa concentration of the second anode composition that is higher than theconcentration proximate the outer surface of the first electrode; andportions of the first electrode 18 between the outer surface and theinner portion continuously transition between the first composition andthe second composition along the radius of the first electrode 18.

In other embodiments, the characteristic gradient may be defined by twoor more discrete regions, wherein each region has consistent materialcharacteristics therein. The discrete regions may be formedsimultaneously and/or in series. For example, as shown in FIG. 3 , whichis a side cross-sectional view of an electrochemical cell according tovarious embodiments, the first electrode 18 may comprise a first portion18 a and a second portion 18 b. As shown in FIG. 3 , the first portion18 a may be located between the outer surface of the first electrode 18and the second portion 18 b. Accordingly, the second portion may belocated between the first portion 18 a and the inner portion of thefirst electrode 18 (e.g., adjacent the current collector 44). Thus, thefirst portion 18 a may define a hollow tubular shape defining anexterior surface coexistent with the exterior surface of the firstelectrode 18, and an interior surface surrounding an open interior ofthe first portion 18 a. The second portion 18 b may be positioned withinthe interior opening of the first portion 18 a, such that the secondportion 18 b defines an exterior surface located adjacent the interiorsurface of the first portion 18 a, and an interior portion coexistentwith the interior portion of the first electrode 18. In variousembodiments, the interface between the first portion 18 a and the secondportion 18 b (defined between the exterior surface of the second portion18 b and the interior surface of the first portion 18 a) may define adiscrete boundary between the first portion and the second portion.However, in certain embodiments, the interface between the first portion18 a and the second portion 18 b may be defined by a mixing regiondefined by intermixing between the first portion 18 a and the secondportion 18 b.

In certain embodiments, the first portion 18 a may define between about20 wt %-80 wt % of the total weight of the first electrode 18, and thesecond portion 18 b may define between about 20 wt %-80 wt % of thetotal weight of the first electrode 18. In example embodiments asdiscussed herein, the weight of the first anode portion 18 a may exceedthe weight of the second anode portion 18 b.

Although not shown in FIG. 3 , the first electrode 18 of variousembodiments may comprise more than two discrete portions. The additionalportions may be located between the first portion 18 a and the secondportion 18 b, thereby forming a series of rings (e.g., concentric rings)surrounding the second portion 18 b and within the first electrode 18.As will be discussed in greater detail herein, the various discreteportions of the first electrode 18 may be coextruded into theelectrochemical cell, the various discrete portions may be extruded intothe electrochemical cell in series, and/or the like.

As just one example, the surfactant within the first portion 18 a may bedifferent than the surfactant within the second portion 18 b.Specifically, the surfactant within the first portion 18 a may cause thefirst portion to have a higher charge transfer resistance and loweranode conductivity than the second portion 18 b. In certain embodiments,the surfactant within the first portion 18 a is a phosphate estersurfactant and the surfactant within the second portion 18 b is asulfonate surfactant. As another example, a nonionic surfactant may beused in one of the first portion 18 a or the second portion 18 b, and ananionic surfactant may be used in the other portion of the anode.Specifically, a first surfactant having a first affinity for adhering tozinc particles may be provided in the first portion 18 a and a secondsurfactant having a second affinity for adhering to zinc particles(e.g., a lower affinity for adhering to zinc particles) may be providedin the second portion 18 b. Such a gradient of surfactant types mayenable zinc plating onto the current collector 44, thereby decreasingoff-gassing, while providing highly active surfactant within the regionof the anode having the highest concentration of zinc oxidation duringhigh-rate discharge.

As another example, the average particle size of the active anodematerial (e.g., zinc) within the first portion 18 a may be larger thanthe average particle size of the active anode material within the secondportion 18 b. As another example, the average quantity of activematerial within the first portion 18 a may be greater than the averagequantity of active material within the second portion 18 b (e.g.,measured as a weight-percentage of the active material relative to thetotal weight of the respective first electrode portion; measured as avolume-percentage of the active material relative to the total weight ofthe respective first electrode portion; and/or the like). As yet anotherexample, the average quantity of surfactant within the second portion 18a may be greater than the average quantity of surfactant within thesecond portion 18 b (e.g., measured as a weight-percentage of thesurfactant relative to the total weight of the respective firstelectrode portion; measured as a volume-percentage of the surfactantrelative to the total weight of the respective first electrode portion;and/or the like).

As yet another example, the type of active material utilized in thefirst portion 18 a may be different than the type of active materialutilized in the second portion 18 b (e.g., different grades of zinc maybe used; zinc purchased from different suppliers may be used; zincretrieved from different zinc mines may be used; zinc having differentaverage porosity may be used; zinc having different surface roughnesscharacteristics may be used; active materials having different alloycompositions may be used (e.g., different alloys may be used indifferent anode portions, those alloys may be selected from thenon-limiting examples of zinc-bismuth alloys, zinc-indium alloys,zinc-aluminum alloys, and/or the like), and/or the like). As a specificexample, a zinc alloy known to be highly reactive may be included in thefirst portion 18 a and a zinc known to be less reactive may be includedin the second portion 18 b to increase high-rate service (in which zincreactivity is generally concentrated near the separator) whiledecreasing off-gassing in the region proximate the current collector 44.

Zinc suitable for use in various embodiments may be purchased from anumber of different commercial sources under various designations, suchas BIA 100, BIA 115. Umicore, S. A., Brussels, Belgium is an example ofa zinc supplier. In a preferred embodiment, the zinc powder generallyhas 25 to 40 percent fines less than 75 microns, and specifically 28 to38 percent fines less than 75 microns. Generally lower percentages offines will not allow desired high rate service to be realized andutilizing a higher percentage of fines can lead to increased gassing. Acorrect zinc alloy is needed in order to reduce negative electrodegassing in cells and to maintain test service results.

In certain embodiments, the amount of zinc present in the negativeelectrode ranges generally from about 62 to about 78 weight percent,desirably from about 64 to about 74 weight percent, and specificallyabout 68 to about, 72 weight percent based on the total weight of thenegative electrode, i.e., zinc, solid zinc oxide, surfactant and gelledelectrolyte.

The solid zinc oxide utilized in various embodiments may be highlyactive in order to increase high rate service such as Digital StillCamera (DSC) service, as well as to increase anode rheology and reduceDSC service variability.

The solid zinc oxide added to the anode specifically has high purity andincludes low levels of impurities that can result in higher zinc gassingand lowered service. The solid zinc oxide specifically contains lessthan 30 ppm iron, less than 3 ppm of silver and arsenic, less than 1 ppmof each of copper, nickel, chromium and cadmium, less than 0.50 ppm eachof molybdenum, vanadium and antimony, less than 0.1 ppm tin and lessthan 0.05 ppm germanium.

In various embodiments, a surfactant added to one or more portions ofthe first electrode 18 may be either a nonionic or anionic surfactant,or a combination thereof. For example, as noted above, a nonionicsurfactant may be added to one portion of the first electrode 18 and ananionic surfactant may be added to another portion of the firstelectrode 18. It has been found that anode viscosity is increased duringdischarge by the addition of solid zinc oxide alone, but is mitigated bythe addition of the surfactant. The addition of the surfactant increasesthe surface charge density of the solid zinc oxide and lowers anodeviscosity as indicated above. Accordingly, adding surfactant to aportion of the anode (e.g., a discrete portion of the anode and/orvarying the concentration of the surfactant within the anode) or addingdifferent surfactants within different portions of the anode may createa charge distribution gradient within the anode.

Use of a surfactant is believed to aid in forming a more porousdischarge product when the surfactant adsorbs on the solid zinc oxide.When the surfactant is anionic, it carries a negative charge and, inalkaline solution, surfactant adsorbed on the surface of the solid zincoxide is believed to change the surface charge density of the solid zincoxide particle surfaces. The adsorbed surfactant is believed to cause arepulsive electrostatic interaction between the solid zinc oxideparticles. It is believed that the addition of surfactant results inenhanced surface charge density of solid zinc oxide particle surface.The higher the Brunauer-Emmett-Teller (BET) surface area of solid zincoxide, the more surfactant can be adsorbed on the solid zinc oxidesurface.

Moreover, the inventors have found that differences in surfactantchemistries may create differences in the anode charge transferresistance and anode conductivity of the anode. As specific examples,the inventors have found that an anode composition comprising aphosphate ester surfactant (e.g., nonionic phosphate ester surfactant)has a higher charge transfer resistance and lower anode conductivitythan an anode composition comprising a sulfonate surfactant (e.g.,anionic sulfonate surfactant). When multiple anode compositions havingdifferences in charge transfer resistance are included within a singlecell, the portion of the anode having the lower charge transferresistance discharges first, before other portions of the anode. Thus,including a first anode composition comprising a phosphate estersurfactant (e.g., a nonionic phosphate ester surfactant) and a secondanode composition comprising a sulfonate surfactant (e.g., an anionicsulfonate surfactant) within a single cell (e.g., within correspondingportions of an anode) causes the second anode composition to dischargebefore the first anode composition.

Given this understanding, anodes according to various embodimentscomprise a plurality of anode compositions, and an anode compositionlocated closest to the current collector 44 has a lower charge transferresistance than an anode composition located closest to the separator14. In such embodiments, the anode composition located closest to thecurrent collector 44 discharges prior to the anode composition locatedat the separator 14, thereby preventing a premature formation of a zincoxide barrier adjacent to the separator 14, which may impede furtherdischarge of anode active material located closer to the currentcollector 44.

The aqueous alkaline electrolyte comprises an alkaline metal hydroxidesuch as potassium hydroxide (KOH), sodium hydroxide, or the like, ormixtures thereof. The alkaline electrolyte used to form the gelledelectrolyte of the negative electrode contains the alkaline metalhydroxide in an amount from about 26 to about 36 weight percent,desirably from about 26 to about 32 weight percent, and specificallyfrom about 26 to about 30 weight percent based on the total weight ofthe alkaline electrolyte. Interaction takes place between the negativeelectrode alkaline metal hydroxide and the added solid zinc oxide, andit has been found that lower alkaline metal hydroxide improves DSCservice. Electrolytes which are less alkaline are preferred, but canlead to rapid electrolyte separation of the anode. Increase of alkalinemetal hydroxide concentration creates a more stable anode, but canreduce DSC service.

A gelling agent may be utilized in the negative electrode as is wellknown in the art, such as a crosslinked polyacrylic acid, such asCarbopol® 940, which is available from Noveon, Inc. of Cleveland, Ohio,USA. Carboxymethylcellulose, polyacrylamide and sodium polyacrylate areexamples of other gelling agents that are suitable for use in analkaline electrolyte solution. Gelling agents are desirable in order tomaintain a substantially uniform dispersion of zinc and solid zinc oxideparticles in the negative electrode. The amount or gelling agent presentis chosen so that lower rates of electrolyte separation are obtained andanode viscosity in yield stress are not too great which can lead toproblems with anode dispensing.

Other components which may be optionally present within one or moreportions of the negative electrode include, but are not limited to,gassing inhibitors, organic or inorganic anticorrosive agents, platingagents, binders or other surfactants. Examples of gassing inhibitors oranticorrosive agents can include indium salts, such as indium hydroxide,perfluoroalkyl ammonium salts, alkali metal sulfides, etc. In oneembodiment, dissolved zinc oxide may be present via dissolution in theelectrolyte, in order to improve plating on the bobbin or nail currentcollector and to lower negative electrode shelf gassing. The dissolvedzinc oxide added is separate and distinct from the solid zinc oxidepresent in the anode composition. Levels of dissolved zinc oxide in anamount of about 1 weight percent based on the total weight of thenegative electrode electrolyte are preferred in one embodiment. Thesoluble or dissolved zinc oxide generally has a BET surface area ofabout 4 m2/g or less measured utilizing a Tristar 3000 BET specificsurface area analyzer from Micrometrics having a multi-point calibrationafter the zinc oxide has been degassed for one hour at 150° C.; and aparticle size D50 (mean diameter) of about 1 micron, measured using aCILAS particle size analyzer as indicated above. In a furtherembodiment, sodium silicate in an amount of about 0.3 weight percentbased on the total weight of the negative electrode electrolyte ispreferred in the negative electrode in order to substantially preventcell shorting through the separator during cell discharge.

Example Method of Manufacture

As mentioned briefly herein, the one or more portions of the anode(e.g., a first portion 18 a of a first electrode 18; a second portion 18b of the first electrode 18; and/or the entirety of the first electrode18) may be extruded to form the first electrode within theelectrochemical cell. In certain embodiments, various portions of thefirst electrode 18 may be co-extruded (e.g., by simultaneously orsuccessively extruding separate portions of the anode via concentricnozzles), extruded in series (extruding a first portion 18 a of thefirst electrode 18 while a die is positioned at least substantiallyconcentrically within the can, removing the die to form an interioropening within the first portion 18 a, and then extruding the secondportion 18 b of the first electrode 18 into the interior opening createdby the removal of the die), 3D-printed (e.g., by extruding successivelayers of the first electrode 18 to form the entire first electrode 18),and/or the like. In certain embodiments, a first anode compositionutilized to form the first portion 18 a may be extruded into theelectrochemical cell, and a forming plunger may then be extended intothe electrochemical cell to form the first portion 18 a of the firstelectrode 18. For example, the forming plunger may form the firstportion 18 a into a general ring shape within an interior of a secondelectrode 12 (e.g., on an opposite side of a separator 44) to define aninterior surface of the first portion 18 a. Thereafter, the secondportion 18 b may be extruded into the interior portion of the firstportion 18 a, bound by the interior surface of the first portion 18 a.

In one embodiment, the zinc and solid zinc oxide powders, and otheroptional powders other than the gelling agent, are combined and mixed.In certain embodiments, the zinc and solid zinc oxide powders may bemixed in separate batches corresponding to various portion of the anode.For example, first zinc and zinc oxide powders may be mixed to form afirst batch and second zinc and zinc oxide powers may be mixed to form asecond batch (e.g., comprising a zinc powder having a different averagezinc particle size than the zinc powder of the first batch).

Afterwards, a surfactant may be introduced into the mixture containingthe zinc and solid zinc oxide (e.g., the surfactant may be introducedinto each of the various batches). A pre-gel comprising alkalineelectrolyte, soluble zinc oxide and gelling agent, and optionally otherliquid components, may be introduced to the surfactant, zinc and solidzinc oxide mixture(s) which are further mixed to obtain a substantiallyhomogenous mixture (e.g., homogeneous within each batch) before additionto the cell. In various embodiments, one or more component of each batchmay be varied to provide a desired anode characteristics differencebetween each batch (e.g., providing a different quantity of surfactant;providing a different zinc grade; providing a different zinc oxidequantity; and/or the like).

In certain embodiments, a surfactant may be introduced into theelectrochemical cell prior to forming the first electrode 18 therein.For example, a surfactant may be mixed with an alkaline electrolyte(e.g., free electrolyte, as discussed herein) to be added to theelectrochemical cell after the second electrode 12 is formed therein,but before the first electrode 18 is added within the electrochemicalcell. In such embodiments, the surfactant may be temporarily absorbed atleast in part by the second electrode 12. Once the first electrode 18 isformed within the interior portion of the second electrode (e.g., viaextrusion) the surfactant may be absorbed by the first electrode 18. Insuch embodiments, the surfactant may be gradually absorbed by the firstelectrode 18, thereby creating a higher concentration of the surfactantat the exterior surface of the first electrode 18 than an inner portionof the first electrode 18 proximate the current collector 44.Accordingly, the surfactant may form an at least substantiallycontinuous concentration gradient within the first electrode 18, whichmay additionally define a charge transfer resistance gradient. It shouldbe understood that the surfactant may form a continuous concentrationgradient within a first electrode 18 having a discrete first portion 18a and second portion 18 b. Accordingly, the first electrode 18 may havea first characteristic gradient defined by the continuous surfactantgradient within the first electrode 18 and may simultaneously have asecond characteristic gradient defined by the step-wise characteristicgradient (e.g., anode alloy composition gradient, average activematerial particle size gradient, average active material concentrationgradient, and/or the like) defined by the first portion 18 a and thesecond portion 18 b.

In a further embodiment, the solid zinc oxide is predispersed in anegative electrode pre-gel comprising the alkaline electrolyte, gellingagent, soluble zinc oxide and other desired liquids, and blended, suchas for about 15 minutes. As mentioned above, multiple batches may beprovided, each comprising the solid zinc oxide, the alkalineelectrolyte, gelling agent, soluble zinc oxide and other desiredliquids. In certain embodiments, each batch may comprise a differentcomposition of the combined components, as mentioned above. The solidzinc and surfactant are then added and each batch of the negativeelectrode composition is blended for an additional period of time, suchas about 20 minutes. The amount of gelled electrolyte utilized in eachbatch the negative electrode composition is generally from about 25 toabout 35 weight percent. For example, the amount of gelled electrolytemay be about 32 weight percent based on the total weight of each batchof negative electrode composition. Volume percent of the gelledelectrolyte may, in certain embodiments, be about 70% based on the totalvolume of the negative electrode. In addition to the aqueous alkalineelectrolyte absorbed by the gelling agent during the negative electrodemanufacturing process, an additional quantity of an aqueous solution ofalkaline metal hydroxide, i.e., “free electrolyte”, may also be added tothe cell during the manufacturing process. The free electrolyte may beincorporated into the cell by disposing it into the cavity defined bythe positive electrode or negative electrode, or combinations thereof.In one embodiment, free electrolyte is added both prior to addition ofthe negative electrode mixture as well as after addition. In oneembodiment, about 0.97 grams of 29 weight percent KOH solution is addedto an LR6 type cell as free electrolyte, with about 0.87 grams added tothe separator lined cavity before the negative electrode is inserted. Asdiscussed herein, the free electrolyte added prior to insertion of thenegative electrode may comprise a surfactant composition that is laterabsorbed by the negative electrode, thereby forming a surfactantconcentration gradient within the negative electrode. The remainingportion of the 29 weight percent KOH solution is injected into theseparator lined cavity after the negative electrode has been inserted.

In certain embodiments, the one or more batches of negative electrodecomposition may be combined prior to forming the negative electrodewithin the electrochemical cell. For example, the one or more batches ofnegative electrode composition may be combined via a single-screwextrusion mixer, a dual-screw extrusion mixer, and/or the like. Invarious embodiments, the one or more batches of negative electrodecomposition may be combined to form a gradient between various portionsof the negative electrode. For example, the one or more batches ofnegative electrode composition may be combined via a mixing component(e.g., a screw extrusion mixer) that enables at least a portion of eachbatch of negative electrode composition to pass along sides of themixing component without being blended. In certain embodiments, thevarious batches may be blended to form a continuous gradient betweenportions of the negative electrode. For example, as discussed herein,the various batches may be blended and ultimately extruded or otherwiseformed within the electrochemical cell such that the negative electrodedefines a gradient of electrode characteristics between the formed outersurface of the negative electrode and the formed interior portion of thenegative electrode.

In other embodiments, the one or more batches of negative electrodecomposition may be kept separate until forming the first electrode 18within the electrochemical cell. In such embodiments, the one or morebatches may be coextruded through separate nozzles to form the firstelectrode 18. The separate nozzles may be at least partially concentricand configured to form concentric portions of the first electrode 18. Inother embodiments, a first batch (e.g., destined to form the firstportion 18 a of the negative electrode) may be extruded into theelectrochemical cell, and a plunger, mold, or other forming componentmay be extended into the electrochemical cell to form the first portion18 a of the negative electrode within the electrochemical cell. Afterforming the first portion 18 a, the second batch may be extruded intothe electrochemical cell and into an interior opening that is at leastsubstantially concentric with the first portion 18 a (e.g., using thesame nozzle or a different nozzle than the first batch) to form thesecond portion 18 b. In certain embodiments, one or more additionalportions (e.g., intermediate portions between the first portion 18 a andthe second portion 18 b) may be extruded into the electrochemical celland formed into corresponding portions prior to the formation of thesecond portion 18 b, each of these additional portions may be formed ina manner similar to that discussed in reference to the first portion 18a.

Second electrode 12, also referred to herein as the positive electrodeor cathode, may include manganese dioxide as the electrochemicallyactive material. Manganese dioxide is present in an amount generallyfrom about 80 to about 86 weight percent, such as from about 81 to 85weight percent by weight based on the total weight of the positiveelectrode, i.e., manganese dioxide, conductive material, positiveelectrode electrolyte and additives such as barium sulfate. Manganesedioxide is commercially available as natural manganese dioxide (NMD),chemical manganese dioxide (CMD), or electrolytic manganese dioxide(EMD). The preferred manganese dioxide for use in a cell is EMD.Suppliers of EMD include Tronox Ltd. of Stamford, Conn.; TosohCorporation of Tokyo, Japan, and Erachem Comilog, Inc. of Baltimore, Md.The positive electrode is formed by combining and mixing desiredcomponents of the electrode followed by dispensing a quantity of themixture into the open end of the container and then using a ram to moldthe mixture into a solid tubular configuration that defines a cavitywithin the container in which the separator 14 and first electrode 18are later disposed. Second electrode 12 has a ledge 30 and an interiorsurface 32 as illustrated in FIG. 1 . Alternatively, the positiveelectrode may be formed by pre-forming a plurality of rings from themixture comprising manganese dioxide and then inserting the rings intothe container to form the tubular-shaped second electrode. The cellshown in FIG. 1 would typically include 3 or 4 rings.

The positive electrode can include other components such as a conductivematerial, for example graphite, that when mixed with the manganesedioxide provides an electrically conductive matrix substantiallythroughout the positive electrode. Conductive material can be natural,i.e., mined, or synthetic, i.e., manufactured. In one embodiment, thecells include a positive electrode having an active material or oxide tocarbon ratio (O:C ratio) that ranges from about 12 to about 14. Too highof an oxide to carbon ratio decreases the container to cathoderesistance, which affects the overall cell resistance and can have apotential effect on high rate tests, such as the DSC test, or highercut-off voltages. Furthermore the graphite can be expanded ornon-expanded. Suppliers of graphite for use in alkaline batteriesinclude Imerys Graphite & Carbon in Bironico, Switzerland and SuperiorGraphite in Chicago, Ill. Conductive material is present generally in anamount from about 5 to about 10 weight percent based on the total weightof the positive electrode. Too much graphite can reduce manganesedioxide input, and thus cell capacity; too little graphite can increasecontainer to cathode contact resistance and/or bulk cathode resistance.An example of an additional additive is barium sulfate (BaSO₄), which iscommercially available from Bario E. Derivati S.p.A. of Massa, Italy.The barium sulfate is present in an amount generally from about 1 toabout 2 weight percent based on the total weight of the positiveelectrode. Other additives can include, for example, barium acetate,titanium dioxide, binders such as coathylene, and calcium stearate.

In one embodiment, the positive electrode component, such as themanganese dioxide, conductive material, and barium sulfate are mixedtogether to form a homogeneous mixture. During the mixing process, analkaline electrolyte solution, such as from about 37% to about 40% KOHsolution, is evenly dispersed into the mixture thereby insuring auniform distribution of the solution throughout the positive electrodematerials. The mixture is then added to the container and moldedutilizing a ram. Moisture within the container and positive electrodemix before and after molding, and components of the mix may be optimizedto allow quality positive electrodes to be molded. Mix moistureoptimization allows positive electrodes to be molded with minimal splashand flash due to wet mixes, as well as spalling and excessive tool weardue to dry mixes, with optimization helping to achieve a desired highcathode weight. Moisture content in the positive electrode mixture canaffect the overall cell electrolyte balance and has an impact on highrate testing.

Separator 14 is provided in order to separate first electrode 18 fromsecond electrode 12. Separator 14 maintains a physical dielectricseparation of the positive electrode's electrochemically active materialfrom the electrochemically active material of the negative electrode andallows for transport of ions between the electrode materials. Inaddition, the separator acts as a wicking medium for the electrolyte andas a collar that prevents fragmented portions of the negative electrodefrom contacting the top of the positive electrode. Separator 14 can be alayered ion permeable, non-woven fibrous fabric. A typical separatorusually includes two or more layers of paper. Conventional separatorsare usually formed either by pre-forming the separator material into acup-shaped basket that is subsequently inserted under the cavity definedby second electrode 12 and closed end 24 and any positive electrodematerial thereon, or forming a basket during cell assembly by insertingtwo rectangular sheets of separator into the cavity with the materialangularly rotated 90° relative to each other. Conventional pre-formedseparators are typically made up of a sheet of non-woven fabric rolledinto a cylindrical shape that conforms to the inside walls of the secondelectrode and has a closed bottom end.

The foregoing configurations address common discharge deficienciesassociated with existing alkaline-cell batteries operating at highdischarge rates. Through experimentation, it has been found thattraditional alkaline cells do not entirely discharge when the cells aresubject to high discharge rate usage. Specifically, it has been foundthat oxidation of zinc within the anode that causes the formation of ZnOis concentrated near the separator during high-rate discharge ofalkaline cells containing generally homogeneous anodes. As mentionedabove, because the ZnO has a higher particle volume than unreacted zinc,the ZnO formation near the separator effectively creates a barrier thatimpedes discharge of zinc particles positioned closer to the center ofthe anode.

Accordingly, by providing an anode characteristic gradient, thecharacteristics of the anode may be modified to encourage a lowerdischarge resistance within anode portions closer to the central currentcollector (and away from the separator), which may increase the quantityof zinc available near the separator after certain depth of thedischarge during moderate- and high-rate discharge of the cell. Forexample, different surfactant types may be provided in portions of theanode proximate the separator and proximate the current collector tospread out the current distribution so that a higher percentage of theanode active materials within the anode participate in the dischargereactions; a larger average particle size of anode active material maybe disposed proximate the separator (e.g., to avoid the completeconsumption of the zinc near the separator during moderate and high ratedischarge); and/or the like. Moreover, the portions of the anode closerto the current collector may be modified to have decreased gassingcharacteristics, thereby reducing undesirable gassing when the anode ishighly discharged.

By providing a characteristic gradient within the anode, the overallelectrical capacity of the anode may remain substantially unchangedrelative to traditional, homogenous anode formulations, however theportions of the anode known to discharge more quickly in high-ratedischarge applications may be modified to increase the electricalcapacity of the anode in those regions. Because the overall electricalcapacity of the anode remains substantially unchanged relative tohomogenous anode formulations, an anode defining a characteristicgradient theoretically has similar low-rate discharge performancesimilar to traditional homogenous anode formulations.

Experimental Tests

The benefits of use of a dual-anode were shown in experimental tests.Specifically, experimental tests were performed to test the performanceof dual-anode configurations in the Digital Still Camera (DSC) test(measuring the number of photos that may be taken on a single charge ofa battery using a standard digital still camera) and 750 mA personalGrooming test (according to which cells are discharged at a rate of 750mA for 2 minutes each hour, for a period of 8 hours per day, until thecell reaches a cutoff voltage of 1.1V). The test results are shown inFIG. 4 .

In the tests, control alkaline batteries having bobbin-styleconstructions were constructed including a traditional, homogeneousanode configuration having at least substantially uniformcharacteristics throughout the entire anode volume. The control alkalinebatteries included 6.3 grams of anode with 20 ppm of a phosphate estersurfactant.

Experimental alkaline batteries were also constructed having adual-anode configuration. All other characteristics of the batteries,other than those noted below, were identical to the control alkalinebatteries. The experimental alkaline batteries included a dual-anodeconfiguration comprising a first anode portion located adjacent to aseparator and a second anode portion located adjacent to a centrallylocated current collector. Thus, the first anode portion and the secondanode portion were concentric, with the first anode portion surroundingan exterior of the second anode portion. No separator was locatedbetween the first anode portion and the second anode portion. The firstanode portion (located adjacent to the separator) comprisesapproximately 3.6 grams of anode with 20 ppm the phosphate estersurfactant, and the second anode portion (located adjacent to thecurrent collector) comprises approximately 2.7 grams of anode with 20ppm of a sulfonate surfactant. The anode with the sulfonate surfactanthas a lower charge transfer resistance and a higher conductivity ascompared with the anode with the phosphate ester surfactant, so theanode discharge is forced to start from the inside of the anode (withinthe second anode portion located adjacent the current collector).

The results shown in FIG. 4 are standardized relative to the performanceof the control alkaline battery. As shown therein, the experimental dualanode alkaline battery performed 15% better than the control battery inthe DSC test (i.e., the experimental alkaline battery was sufficient tocomplete 115% of the number of photos taken by the control battery), andthe experimental dual anode alkaline battery performed 9% better thanthe control battery in the 750 mA personal Grooming test.

CONCLUSION

Many modifications and other embodiments of the inventions set forthherein will come to mind to one skilled in the art to which theseembodiments pertain having the benefit of the teachings presented in theforegoing descriptions and the associated drawings. Therefore, it is tobe understood that the embodiments are not to be limited to the specificembodiments disclosed and that modifications and other embodiments areintended to be included within the scope of the appended claims.Although specific terms are employed herein, they are used in a genericand descriptive sense only and not for purposes of limitation.

That which is claimed:
 1. An anode defining an anode outer surface and acentral portion, the anode configured to be disposed relative to acathode such that the anode outer surface is adjacent to the cathode andseparates the central portion from the cathode, wherein the anodecomprises: a first anode portion defining the anode outer surface,wherein the first anode portion consists of a first anode formulation; asecond anode portion located at the anode central portion, wherein thesecond anode portion consists of a second anode formulation; the firstanode formulation comprises a higher concentration of a first surfactantcompared to the second anode formulation and the second anodeformulation comprises a higher concentration of a second surfactantcompared to the first anode formulation, wherein the first surfactant isa nonionic surfactant and the second surfactant is an anionicsurfactant; and a total charge transfer resistance within the anode isat least proportional to a separation distance from the cathode andincreases continuously for at least a portion of the anode.
 2. The anodeof claim 1, wherein the first surfactant comprises a phosphate estersurfactant and the second surfactant comprises a sulfonate surfactant.3. The anode of claim 1, wherein the first anode portion is separatedfrom the second anode portion by a characteristic gradient between thefirst anode portion and the second anode portion.
 4. The anode of claim3, wherein the characteristic gradient comprises the first anodeformulation and the second anode formulation, and wherein the proportionof the first anode formulation to the second anode formulation is atleast substantially proportional to the separation distance from thecathode.
 5. The anode of claim 4, wherein the characteristic gradient iscontinuous between the central portion of the anode and the anode outersurface.
 6. The anode of claim 1, wherein a quantity of the first anodecomposition exceeds a quantity of the second anode composition withinthe anode.
 7. The anode of claim 1, wherein the first anode portion hasa first charge transfer resistance and the second anode portion has asecond charge transfer resistance that is lower than the first chargetransfer resistance.
 8. The anode of claim 7, wherein the first anodeformulation comprises an amount of the first surfactant configured tocause the first anode portion to have the first charge transferresistance and the second anode formulation comprises an amount of thesecond surfactant that is different from the amount of the firstsurfactant and configured to cause the second anode portion to have thesecond charge transfer resistance.